Steve,
I was just on the phone with Canon Tech Support for an unrelated issue, and they recommended I update to the most recent driver and firmware. For the two driver versions that are shown (2.42 and 2.70), they said 2.42 was for MacOS 10.6 and earlier, and 2.70 is for MacOS 10.7.
For the order they recommended upgrading the driver first, then the firmware, for what it's worth.
David